With the arrival of the Anthropocene we must now be suspicious of all ideas developed in the last 10,000 years. That includes James Lovelock’s notion of Gaia which, it turns out, is a child of the Holocene. In his recent book, On Gaia, Toby Tyrell shows that since Lovelock put his idea into the world some 30 years ago our understanding of the Earth system has changed dramatically.

As Earth scientists have found means of taking a more fine-grained view of Earth history, especially through the analysis of ice-cores, the trajectory of Earth appears much more wild and unpredictable. There is no built-in stabiliser; life does not bring the planet back into equilibrium. Gaia is based on old science.

(I love that first line!) Now, I haven't read Tyrell's book but I think one point needs to be made: while Earth system science has moved on in the past thirty years so has Lovelock's take on Gaia. It is true that the original hypothesis posited the Earth as a homeostatic system but that notion of homeostasis has long since been abandoned. 'Gaia' has evolved. Lovelock now well understands that there is no equilibrium as such, only an indefinitely large range of quasi-stable states within a complex system; strange attractors and so on. This is not the same thing as 'homeostasis.' The possibility of a sudden and massive system state shift in response to a relatively minor degree of perturbation is precisely the point of his more recent works. That is why Gaia is 'vengeful.'

Here is how Lovelock differentiates the hypothesis and the theory in the glossary to Revenge of Gaia (p.208):

Gaia Hypothesis
James Lovelock and Lynn Margulis postulated in the early 1970s that life on Earth actively keeps the surface conditions always favourable for whatever is the contemporary ensemble of organisms. When introduced it was contrary to the conventional wisdom that life adapted to planetary conditions as it and they evolved in their separate ways. We now know that both the hypothesis as originally stated and the conventional wisdom were wrong. The hypothesis evolved into what is now Gaia Theory and the conventional wisdom into Earth System Science.

Gaia Theory
A view of the Earth that sees it as a self-regulating system made up from the totality of organisms, the surface rocks, the ocean and the atmosphere tightly coupled as an evolving system. The theory sees this system as having a goal—the regulation of surface conditions so as always to be as favourable as possible for contemporary life. It is based on observations and theoretical models; it is fruitful and has made ten successful predictions.

The hypothesis is not the theory and while I am in no position to scientifically defend either this is worth noting.

While, as I say, I've not read Tyrell's book, this interview on his publisher's website makes for interesting reading. Tyrell makes the case, albeit briefly, that Gaia is simply anthropocentric wishful thinking and should be rejected as a scientific idea:

Q: If the Gaia hypothesis is not the reason, then why did the Earth remain habitable for such an enormously long interval of time?

A: This may relate partly to the weak Anthropic Principle, whereby we logically cannot observe any facts that preclude our own existence. So however infrequent it may be in the universe for a planet to remain continuously habitable over billions of years, we happen to be on just such a planet. According to this way of thinking, Earth may just have been lucky, with no sentient observers having evolved on other planets which were not so lucky, i.e. where conditions became sterile at some point. Another possible explanation for extended habitability in the absence of Gaia is a predominantly inorganic thermostat, such as has been suggested for silicate weathering.

This is a provocative and contestable claim. However, his concluding remarks are if anything more revealing than his central thesis:

Q: Are there any implications for the current era of global change?

A: Yes, it is suggested that belief in the Gaia hypothesis can lead to excessive complacency about the robustness and resilience of the natural system. Gaia emphasizes stabilising feedbacks and protective mechanisms that keep the environment in check. If Gaia is rejected, however, we are left with a less comforting view of the natural system. Without Gaia it is easier to appreciate that the natural system contains lines of weakness and other susceptibilities. One such line of weakness that has already been demonstrated is the ozone layer depletion by CFC’s. I have argued in the book that there is no over-riding Gaia to protect our planet’s life support system. Maintaining the Earth’s environment is up to us [emphasis added].

Who is the Modern here? I don't think that it's Lovelock... To suggest that Gaia is a 'comforting' theory is to be a few decades out of date. Yes, the original might have encouraged worshipful idleness and Nature-absorbed complacency but that is not at all the image of Gaia that is now presented to us. In Gaia Does Not Negotiate Hamilton quotes Latour who is in turn ventriloquising Gaia:

I am not your Mother, nor your protector. … So figure out the enigma of my presence.

The motherly vision of Gaia as homeostatic über-regulator is surely a holocenic fable that has long passed its sell-by-date. However, while, as I've mentioned recently, Lovelock is a tricky ally to enrol I'm not sure that Tyrell is a better option.

Without Gaia what planetary imagery are we left with? 'Spaceship Earth'? Again?...